1. Field of the Invention
The present invention generally relates to a radio base station system and a central control station as well as to a method of processing signals at the central control station
2. Description of the Related Art
FIG. 10 is a block diagram showing a configuration of communication links between mobile-communication base stations.
A central control station 30 (which may be a cluster central control station when base stations having a cluster structure are used) uses a radio communication link 20 and optical communication links 22 and 23 to establish communication links with radio base stations (BS) 31, 32, and 34, respectively. In the case of radio communication, the central control station 30 uses a multiplex/demultiplex equipment (MUX/DEMUX) 44 to supply signals to radio terminals as these signals are supplied from the communication control station. Base-band signals supplied to the terminals are modulated by modems (MODEM2) 401 through 40N, and the resulting signals are converted into radio frequencies by frequency converters (f.Conv.2) 411 through 41N. The output signals of the frequency converters (f.Conv.2) 411 through 41N are combined by a combiner/divider 42. A radio transceiver 43 transmits the combined signal to the radio base station 31.
Between the multiplex/demultiplex equipment 44 and the radio base station 31, modems and frequency converters are provided as many as a necessary maximum transmission capacity can be achieved.
In the case of the optical communication links 22 and 23, the central control station 30 uses the multiplex/demultiplex equipment 44 to supply the signals from the communication control station to terminals for optical communication. The base-band signals are converted by signal converters 451 and 452 into signals having a proper signal format for optical transmission in terms of timings and waveforms. The converted signals are further converted into optical signals by optical transceiver equipment (E/O, O/E) 461 and 462, followed by being transmitted to the base stations 32 and 34 via the optical fibers 22 and 23.
The radio base station 32 uses optical transceiver equipment (O/E, E/O) 1 to convert the signals received from the central control station 30 via the optical fiber 22 into electrical signals, and uses a signal converter 2 to further convert the signals into signals having a proper signal format for modems (MODEM2) 41 through 4N. Multiplex/demultiplex equipment (MUX/DEMUX) 3 demultiplexes the signals, and the resultant signals are converted by the modems 41 through 4N and frequency converters (f.Conv.2) 51 through 5N into modulated signals having a radio frequency that is used between the radio base station (BS) 32 and a radio base station (BS) 33. A combiner/divider 6 combines the modulated signals, and a transceiver (TR2) 7 transmits the combined signal to the radio base station 33.
As in the case of radio communication, the optical communication link that is provided by the optical fiber 22 and extends to the radio base station 32 has a necessary maximum transmission capacity secured for the communication.
FIGS. 11A and 11B are block diagrams showing configurations of transceivers of the radio base stations.
FIG. 11A shows a transceiver of the radio base stations 31 and 33 that exchange radio communications.
A radio receiver/transceiver (TR2) 35 receives a radio signal via an antenna, and a combiner/divider 36 divides the received signal. The frequency converters (f.Conv.2) 371 through 37N convert the divided signals into signals having an intermediate frequency, and modems (MODEM2) 381 through 38N further convert the signals into base-band signals. The base-band signals are multiplexed by multiplex/demultiplex equipment (MUX/DEMUX) 39, which supplies an output signal thereof to a radio transmission circuit (air interface circuit) for transmission from the base station to mobile stations.
FIG. 11B shows a transceiver of the radio base station 34 connected to the central control station 30 through the optical fiber.
A digital signal, after conversion from an optical signal for the optical fiber into an electrical signal, is supplied to a signal converter 47, which convert the signal for optical-fiber digital transmission into a base-band signal for radio communication. The resultant signal is supplied to a radio transmission circuit (air interface circuit) for transmission from the base station 34 to mobile stations.
When communication links between the central control station and the radio base stations varies in their types as shown in the case of FIG. 10, shared use of equipment is difficult because of different transmission formats.
Further, the transmission capacity from the central control station to a radio base station needs to be secured to match a maximum required capacity. Because of this, modems and frequency converters must be provided as many as necessary for each communication link in the case of radio communication, and signal converters and base-band multiplexers need to be provided as many as necessary for each communication link in the case of optical-fiber communication. This may result in an excessive investment in facility.
Accordingly, there is a need for a radio base station system and a central control station which can harmonize transmission formats of radio communication links and optical-fiber communication links, and can gather all the signal converters to the central control station, thereby achieving high overall performance and efficient accommodation of communication lines.